A porn actor has tested positive for HIV at a California clinic, setting off a scramble to track down partners who may have been exposed, and spurring two major production companies to suspend filming.

The actor was a patient of the Adult Industry Medical Healthcare Foundation, a San Fernando Valley clinic that caters to actors in the multibillion-dollar adult entertainment industry. The actor's identity and gender have not been released.

A clinic spokeswoman, Jennifer Miller, told the Los Angeles Times that efforts were under way to notify individuals who may have had sexual contact with the actor.

Wicked Pictures and Vivid Entertainment told the Times that they stopped production as a precaution when the positive test was revealed.

Los Angeles County public health officials and state occupational health officials have said the widespread lack of condom use on porn sets puts performers at risk of contracting HIV and other diseases. Major adult film producers, including Hustler's Larry Flynt, have spoken out against the use of condoms in porn because viewers find them a turnoff.

Last year, a woman tested positive for HIV immediately after making an adult film, and in 2004, an HIV outbreak affecting several actors spread panic in the industry and briefly shut down productions at several California studios.

Porn actors must test negative for HIV and other sexually transmitted diseases within 30 days of going to work on a film.

State workplace safety officials are considering strengthening rules to specify the use of condoms in the adult entertainment industry.

The president of the Aids Healthcare Foundation, Michael Weinstein, said his organisation had been advocating a tightening of the rules.

He said the latest case was the ninth HIV-positive adult film star to be treated at the AIM clinic since the 2004 outbreak.